Research On Improvement And Application Of Critical Slip Field Method

Combined with limit equilibrium method and optimality principle, critical slip field of slope method allows us to find critical slip surfaces quickly、exactly and conveniently as well as the corresponding safety factors. With decades of development, critical slip field method has preliminarily been developed as a new method used in calculation of slope stability, soil pressure and bearing capacity. Based on existing analysis results, in this paper, critical slip field gradually becomes a new geotechnical stability analysis method which is more rigorous、adaptable、functional and universal. The theory of the method is perfected and its application realm is extended,then the improved method has been applied to the stability analysis of engineering application. In addition, based on the modification of normal stresses over slip surface, a new method for the three-dimensional problem of bearing capacity of rectangular shallow footing is proposed.the main works and results are listed as follows:1. According to nonlinear failure characteristic of rock mass, the new analysis method for critical slip field of slope based generalized Hoek-Brown failure criterion is proposed. The Hoek-Brown failure criterion based on the geology strength index (GSI) is one of the most useful criteria in forecasting and computing of rock mass strength. Firstly, the parameters of rock mass strength are obtained by Hoek-Brown failure criterion. Secondly, the shear strength of each point on the Hoek-Brown strength envelope is transferred equivalently to the Mohr-Coulomb linear relation which is tangent to the nonlinear envelope with relevant cohesive and frictional parameters. Finally, the new iterative method is established and the critical slip field of slope by Morgenster-Price method is improved. And then, the most dangerous sliding surfaces are traced according to the principle of maximum thrusts with satisfying both force and moment equilibriums and the corresponding safety factors are calculated quickly and exactly. This method is applied to the stability analysis of two slope examples and the slope in the Xinqiao open-cut pyrite mine. The results show that the present method absorbs the advantages of critical slip field and Hoek-Brown failure criterion and can further considers the nonlinear failure characteristic of slope. The calculation results are well agreed with the practical situation.2. Improvement and extension of critical slip fields of rock slope is performed, in view of the discontinuity of rock. Considering the influence of structural surface on the stability of the slope, a new method is proposed for dealing with structural planes, and tensile cracks are readily introduced based on the tensile strength of rock. This method has been applied to the stability analysis of five example slopes and the slope in the Xinqiao open-cut pyrite mine, and the results prove its accuracy and high efficiency in rock slope stability analysis by compared with those obtained by other methods.3. The process of reservoir water level fluctuation may cause the changes of the slope body in the pore water pressure distribution, which has influences on slope stability. Considering the process of water level changes, a improved numerical simulation method of critical slip field of slope was proposed. Thus, the local and global safety factor of the slope in the process of water changing are obtained conveniently and rapidly. By means of stability analysis of a typical slope in the process of rise and fall in water level and comparing with those by other methods, the results show that the critical slip field method could search for any shape of the most dangerous slip surface, and the safety factor is reasonable.4. The rising of pore water pressure and decreasing of matric suction in the process of the infiltration of rainfall into slope is the main factor of slope failures.Numerical simulation method of critical slip field of slope considering rainfall process is proposed based on proposed unsaturated soil shear strength theory and water pressure field obtained by finite element method analysis of saturated-unsaturated seepage. Thus, slope local safety factor and slope safety factor of the whole as well as the corresponding critical slip surfaces during infiltration were calculated conveniently and rapidly. This method has been applied to the stability analysis of two slope cases and the effect study of rainfall intensity, duration and strength parameter on slope stability, the results show that the critical slip field method could search for any shape of the most dangerous slip surface, and the safety factor is reasonable.5. Numerical methods can be used to calculate stress, strain and failure of slope; but it is difficult to calculate the safety factor of slope stability directly. Limit equilibrium methods can obtain the factor of safety, but they need to assume the interslice forces, which affects the calculation accuracy. Based on the stress field obtained by numerical methods, by defining the maximum thrust forces and improving numerical simulation method of conventional critical slip field of slope, the critical slip field method of slope based on numerical stress field is proposed. The results obtained by using this method for two examples have been compared with other methods. It is shown that the proposed method combines the advantages of numerical method and limit equilibrium method so as to find the critical slip surface of slope accurately and conveniently, and give more reasonable safety factor.6. The improved and expanded calculation method of the critical slip field of slope theory is applied to the stability analysis and evaluation of the slope in the Xinqiao open-cut pyrite mine, the roadbeds of the expressway from Jixi to Huangshan and Jinpingzi Ⅱ section creep mass. Combining with practical situation, reasonable governance recommendations are provided, and the results are satisfactory. It demonstrates that the improved and expanded calculation method consummates the critical slip field of slope theory, expanding its applied range, and enhances the results’ reliability by a wide margin.7. A new method is proposed for three-dimensional analysis of bearing capacity of rectangular shallow footing based on the modification of normal stresses over slip surface. Firstly, the shape of the slip surface is assumed as ellipsoidal, which is composed of a set of log-spirals with different initial radii in the direction on the longer axis of the footing base. Secondly, establishing a method for analysis of bearing capacity of a fixed three-dimensional slip surface, by improving the limit equilibrium solution of3D slope stability based on the modification of normal stresses over slip surface. Finally, the bearing capacity of the footing is the minimum of selected fixed three-dimensional slip surfaces, by changing the position of the pole of log-spirals. Bearing capacity coefficients are then given for calculating the bearing capacity by using the method of the superposition involved in the conventional bearing capacity formula and investigating the effects of the angle of internal friction and the length-width ratio of footing. This method has been applied to calculate the bearing capacity of one example and compared with other methods; the results show its accuracy and reasonable and high effectiveness in three-dimensional bearing capacity analysis of rectangular shallow footing.